The present invention relates to a calibration sensor unit for calibrating an eyeglass lens processing apparatus that processes or finishes a peripheral edge of an eyeglass lens.
An eyeglass lens processing apparatus includes lens chuck shafts for holding an eyeglass lens, a lens chuck shaft rotating mechanism, a rotating mechanism for rotating a processing tool rotating shaft to which a grindstone as a processing tool for processing or finishing the peripheral edge of the eyeglass lens, an X moving mechanism for moving the processing tool and the lens relatively to the axial direction of the lens chuck shafts (an X-axis direction) and a Y moving mechanism for moving the lens chuck shafts in a direction (a Y-axis direction) for changing an axial distance between the lens chuck shafts and the processing tool rotating shaft. In this device, in order to precisely process or finish the peripheral edge of the eyeglass lens by the processing tool such as the grindstone, a positional relation between each processing tool and the lens chuck shafts (positions of the lens chuck shafts in the Y-axis direction and the X-axis direction relative to the processing tool) needs to be calibrated.
As a calibrating technique, a technique is proposed in which a calibrating template having a circular outline in a part is held by a pair of lens chuck shafts in place of an eyeglass lens, a carriage for holding the lens chuck shafts so as to freely rotate is lowered to move the template toward a grindstone, and when the template contacts the grindstone, the movement of the carriage is stopped, so that the stop of the movement of the carriage is detected by a sensor provided in a Y moving mechanism (JP-A-8-318458 (U.S. Pat. No. 5,806,198)). Further, a technique is proposed in which the surface of a processing tool such as a grindstone has an electric conductivity, a holding part of a template is electrically insulated, the surface of the template is formed with an electrically conductive member and a current supplied between the surface of the processing tool and the surface of the template is detected to electrically detect the contact of the processing tool with the template (JP-A-2000-127015 (U.S. Pat. No. 6,327,790)).
Since the rigidity of the lens chuck shafts and the processing tool rotating shaft is not high, when a load is applied thereto, the lens chuck shafts and the processing tool rotating shaft are bent. Especially, in the technique disclosed in JP-A-8-318458 (U.S. Pat. No. 5,806,198), since the contact of the template with the grindstone by the movement of the carriage is detected in accordance with the stop of the lowering movement of the carriage, a stop position includes an error due to the bending of the lens chuck shafts and the processing tool rotating shaft. Particularly, since the processing tool rotating shaft to which a chamfering grindstone with a small diameter or a grooving tool is attached is small and light, the rigidity is low. Further, since the contact of the template with the grindstone is detected under a state that the processing tool rotating shaft is bent, accuracy is more reduced. On the other hand, the technique disclosed in JP-A-2000-127015 (U.S. Pat. No. 6,327,790) is proposed as an improvement of the technique disclosed in JP-A-8-318458 (U.S. Pat. No. 5,806,198), however, the processing tool such as the grindstone needs to have the electric conductivity and the technique cannot be employed in a processing tool having no electric conductivity. Further, the processing tool is rotated at high speed by a rotating mechanism having a bearing for holding the processing tool rotating shaft so as to freely rotate. When the rotating mechanism such as the bearing does not have the electric conductivity, the technique disclosed in JP-A-2000-127015 (U.S. Pat. No. 6,327,790) cannot be used. Further, since a ball arranged in the bearing contacts the rotating shaft, a current may not be necessarily stably supplied. When the flow of the current in the processing tool rotating mechanism is unstable, the contact of the calibrating template with the grindstone cannot be precisely detected.